Paper I
Question
Transduction
Answer
Transduction is a mechanism of horizontal gene transfer in which bacterial DNA is transferred from one bacterium (donor) to another (recipient) via a bacteriophage acting as the vector.
Types:
- Generalized transduction: occurs during the lytic cycle of a virulent phage. During assembly of new phage particles, the packaging machinery occasionally makes an error and packages a random fragment of the host bacterial chromosome instead of (or along with) phage DNA. When this defective phage particle infects a new recipient bacterium, it injects the packaged bacterial DNA, which can then recombine into the recipient’s chromosome — any bacterial gene can potentially be transferred, hence “generalized.”
- Specialized (restricted) transduction: occurs with temperate (lysogenic) phages, which integrate as a prophage at a specific chromosomal site during lysogeny. On induction (excision to re-enter the lytic cycle), imprecise excision can carry adjacent bacterial genes (only those flanking the specific integration site) along with the phage genome into new phage particles — hence “specialized,” since only genes near the attachment site can be transferred this way.
Clinical/biological significance: transduction transfers genes for toxin production (lysogenic/phage conversion — e.g., diphtheria toxin in toxigenic Corynebacterium diphtheriae, erythrogenic toxin in Streptococcus pyogenes, Shiga-like toxin in certain E. coli strains, all encoded by a prophage carried by the bacterium) as well as antibiotic-resistance genes, contributing to bacterial pathogenicity and the spread of drug resistance.